Analysis of Caffeine by Liquid Chromatography-Mass Spectrometry - Caffeine: Chemistry, Analysis, Function and Effects - page 113

quantitative analysis of environmental samples by LC-MS-MS as signal sup-
pression or enhancement can compromise the accuracy of analytical results.
Zhao and Metcalfe (2008) approached this subject by determining the effects
of sample matrix on the analysis of six neutral pharmaceuticals, including
caffeine, in samples of municipal wastewater using LC-APCI-MS-MS. They
also evaluated whether isotope-labeled internal standards could be used to
compensate for matrix effects. Wastewater samples were filtered, applied onto
solid-phase extraction (SPE) cartridges and the eluates were concentrated.
Samples were then spiked with isotope-labeled internal standards, including
caffeine- 13 C 3 . The analytes were separated on a C18 column using a mobile
phase consisting of a gradient of 10 mM ammonium acetate and acetonitrile.
MS determination was performed using a quadrupole-linear trap instrument
equipped with an APCI source. Multiple reaction monitoring (MRM) in the
positive ion mode was used for quantification (m/z transition 195 A 138, in the
case of caffeine). Isotope-labeled compounds corrected for overestimates that
occurred as a result of interferences from the sample matrix.
Conley et al (2008) also used LC-MS-MS for the analysis of caffeine,
together with another 12 different pharmaceuticals and one metabolite in
surface water at low ng L -1 levels. Pharmaceuticals were chosen based on the
estimated usage rate inferred from the number of prescriptions dispensed per
year in the US, and commonly consumed non-prescription drugs. Sample
preparation conditions were similar to those described by Zhao and Metcalfe
(2008). Separation of compounds were performed on a bridged-ethyl-siloxane-
silica hybrid C18 ultra-performance liquid chromatography (UPLC) column
using a step-wise binary elution gradient consisting of 0.1% aqueous formic
acid and acetonitrile. For detection, a triple quadrupole MS fitted with an ESI
source operated in the positive mode was employed.
Very recently, Wang et al (2011) developed and validated a comprehensive
LC-MS-MS method for the simultaneous analysis of caffeine and another 15
pharmaceutical compounds, including antibiotics, hormones, analgesics,
stimulants, antiepileptics, and X-ray contrast media, in two different water
matrices. A quadrupole-linear trap MS equipped with an ESI source was
employed in both positive and negative modes for the detection of analytes and
their quantification was performed by MRM.
A slightly different approach was addressed by Huerta-Fontela et al (2007),
who used UPLC-MS-MS to analyze simultaneously 15 stimulatory drugs in
water. In addition to caffeine and nicotine, which are non-controlled drugs,
they studied controlled drugs such as cocaine, amphetamine-related com-
pounds, lysergic acid, ketamine, and fentanyl. Metabolites of these stimulatory
drugs were also investigated. Using a bridged-ethyl-siloxane-silica hybrid C18
UPLC column with gradient elution (0.1% aqueous formic acid and
acetonitrile), chromatographic separation was achieved in less than 4.5 min.
Detection was performed by a triple quadrupole MS equipped with an ESI
source working in positive mode. Quantification and confirmation MRM m/z
transitions for caffeine were 195 A 138 and 195 A 110, respectively.

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